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Microbiology > 9. Viruses > Flashcards

9. Viruses Flashcards

1
Q

virus

A

obligate intracellular parasite
genetic element that cannot replicate independently of a living (host) cell
intracellular form

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2
Q

virus particle (virion)

A

extracellular form of a virus
-exists outside host and facilitate transmission from one host cell to another

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3
Q

replication/ reproduction occurs only upon

A

infection
entry into host cell

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4
Q

viruses can infect all cell types

A

bacterial viruses called bacteriophages (phages)
few archaeal viruses
most are eukaryotic viruses

classified into families based on:
-genome structure (DNA or RNA)
-life cycle
-morphology
-genetic relatedness

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5
Q

structure of viruses

A

all virions contain a nucleocapsid which is composed of nucleic acid (DNA or RNA) and a protein coat (capsid)
-some viruses consist only of a nucleocapsid, others have additional components (envelopes)

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6
Q

capsids

A

large macromolecular structures which serve as protein coat of virus

protect viral genetic material and aid in its transfer between host cells

made of protein subunits called protomers

capsids are helical, cosahedral, or complex

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7
Q

helical capsids

A

-shaped like hollow tubes with protein walls
-protomers self assemble
-length of capsid is a function of nucleic acid

*naked is harder to control- no lipid bilayer
*phospholipid bilayer can be targeted by disinfectants (enveloped)

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8
Q

icosahedral capsids

A

an icosahedron is a regular polyhedron with 20 equilateral faces and 12 vertices

capsomers
-ring or knob-shaped units made of 5 or 6 protomers
-pentamers - 5 subunit capsomers
-hexamers- 6 subunit capsomers

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9
Q

viral envelopes and enzymes

A

many viruses are bound by an outer, flexible, membranous layer called the envelope

animal virus envelopes (lipids and carbohydrates) usually arise from host cell plasma or nuclear membranes

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10
Q

viral envelope proteins

A

envelope proteins (involved in attachment) which are viral encoded, may project from the envelope surface as spikes (identification) or peplomers
1. involved in viral attachment to host cell
2. used for identification of virus (spike proteins)
3. may have enzymatic or other activity (neuraminidase of influenza virus- enable virus to escape from host cell)
4. may play a role in nucleic acid replication

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11
Q

structure of the virion

A

enzymes inside virions
1. lysozyme
2. neuraminidase
3. nucleic acid polymerases (RNA replicases: RNA-dependent RNA polymerases)

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12
Q

lysozyme

A

-makes hole in cell wall to allow nucleic acid entry
-also lyses bacterial cell to release new virions

*break down peptidoglycan (in bacteriophages)

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13
Q

neuraminidases

A

part of viral envelope
-destroy glycoproteins and glycolipids
-allows liberation of viruses from cell

animal virus –> escape

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14
Q

nucleic acid polymerases

A

RNA replicases: RNA-dependent RNA polymerases
reverse transcriptase: RNA-dependent DNA polymerase in retroviruses (RNA - DNA - RNA)

only found in RNA viruses

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15
Q

viral genomes are structurally diverse

A

-single or double stranded DNA or RNA
-the length of the nucleic acid also varies from virus to virus
-genomes can be linear or circular (some RNA viruses have segmented genomes)

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16
Q

phases of viral replication in a permissive (supportive) host

A

attachment (the most important step)
penetration
synthesis
assembly
release

17
Q

attachment (adsorption)

A

specific receptor attachment
receptor determines host preference:
-may be specific tissue (tropism)
-may be more than one host
-may be more than one receptor

18
Q

entry into the host

A

entire genome or nucleocapsid
varies between naked or enveloped virus
three methods used:
1. fusion of the viral envelope with host membrane; nucleocapsid enters (animal virus)
2. endocytosis in vesicle: endosome aids in viral uncoating (animal virus)
3. injection of nucleic acid (phages)

19
Q

bacterial and archaeal viral infections

A

virulent phage
temperate phage

20
Q

virulent phage

A

one reproductive choice
-multiplies immediately upon entry
-lyses bacterial host cell

21
Q

temperate phage

A

two reproductive options
-reproduce lytically as virulent phages do
-remain within host cell without destroying it
-many temperate phages integrate their genome into host genome (becoming a prophage in a lysogenic bacterium) in a relationship called lysogeny

lysogenic only for bacteriophages

22
Q

overview of animal virus infection

A

-major tenets (capsid and DNA/RNA genome, infection and takeoverof host, assembly and release) univeral
-classified by genomes (RNA or DNA)
-most human viral diseased are caused by RNA viruses

23
Q

two key differences of animal virus infection

A
  1. entire virion enters the animal cell
  2. eukaryotic nucleus is the site of replication for many animal viruses
24
Q

animal virus entry mechanisms

A
  1. fusion
  2. enveloped endocytosis
  3. non-enveloped endocytosis
25
Q

animal virus infection

A

viral infection of animal cells
-uncoating occurs at cytoplasmic membrane or cytoplasm
-viral DNA genomes enter nucleus, most viral RNA is converted to DNA within nucleocapsid
–bind specific host cell receptors, typically used for cell-cell contact or immune function

26
Q

virion release (animal)

A

nonenveloped viruses lyse the host cell
-viral proteins may attack peptidoglycan or membrane

enveloped viruses use budding
-viral proteins are incorporated into host membrane
-nucleocapsid may bind to viral proteins
-envelope derived from host plasma membrane, but may be Golgi, ER, or other
-virus may use host actin tails to propel through host membrane

27
Q

animal virus infection- cellular outcomes

A
  1. transformation (tumor cell division)
  2. lysis (death of the cell and release of virus)
  3. persistent infection (slow release of virus without causing cell death)
  4. latent infection (virus present but not replicating)
28
Q

hosts for bacterial and archaeal viruses

A

usually cultivated in broth or agar cultures of suitable, young, actively growing bacteria

broth cultures lose turbidity as viruses reproduce

plaques observed on agar cultures

29
Q

hosts for animal viruses

A

tissue (cell) cultures
-cells are infected with virus
-bacteriophages- localized area of cellular destruction and lysis that enlarge as the virus replicates

cytopathic effects
embryonated eggs

30
Q

prions

A

neurodegenerative diseases in humans and animals

31
Q

virus classification

A

ds vs ss
symmetry
presence/ absence envelope
dimensions

Microbiology (8 decks)

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